The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Emissions of a vehicle contain harmful materials such as carbon monoxide (CO), nitrogen oxides (NOx), hydrocarbons (HC), and the like. Among these three elements generated during the combustion process, NOx always has the opposite causal relationship with respect to CO and HC.
That is, the largest portion of NOx is generated at a point in time at which CO and HC are reduced in a practical output range. The generation of NOx is increased as fuel is completely burnt, that is, as an engine has a higher temperature.
Thus, emission allowance has been regulated as the relevant Act, and thus, various technologies have been developed to reduce emissions. Among those technologies is an exhaust gas recirculation (EGR).
According to the EGR, a partial amount of previous combustion gas (EGR gas) is supplied to a mixture intaken to a combustion chamber, while maintaining a mixing ratio as a theoretical air-fuel ratio, in order to reduce generation of NOx without rapidly increasing other harmful materials. That is, the EGR is a device used to lower a temperature of flame by increasing heat capacity of such a combustion gas.
In detail, the EGR is for recirculating an exhaust gas of the discharge gas to an intake system to lower a combustion temperature of an interior of a cylinder to suppress generation of NOx. In other words, as a means for reducing NOx of the exhaust gas, the EGR returns a partial amount of exhaust gas to the intake system to lower a highest temperature when a mixture is burnt, thus reducing generation of NOx.
Among components of the EGR system, an EGR cooler is a sort of heat-exchanger cooling an exhaust gas having a high temperature by a coolant of an engine as a refrigerant. In order to cool the EGR cooler, the EGR cooler is mounted outside of a cylinder block or outside of the engine so as to be cooled.